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MF 12 dies when key switch is released from "start" to "on"


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#1 captweiner OFFLINE  

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Posted May 24, 2018 - 09:50 PM

I have an older MF 12 (coil and points) that has ran for 2 years and will not this spring. 

 

Starts excellent but when you let go of the key (releasing back to "on") it dies.

 

The wiring setup that worked and no longer does is the following...(I realize being 50 years old this might not be "factory" however it did work up to now)

 

The key switch has 3 spades but there are no labels....if they did exist rust has removed them.

 

One spade goes to the hot large post on the solenoid (same one as positive battery cable)

 

One spade has two wires on it with one going to a small post on the solenoid (solenoid has two small/two large posts) and other wire going to positive post on coil.

 

Third post has no wires hooked to it.

 

Any ideas....as this setup was how I purchased tractor and it ran the last two years.

 

It appears to kill spark when releasing from start to on.....does this mean bad switch?

 

I bought a new switch but it is 5 post and I am not sure how to wire it as the current switch only used two posts.



#2 John Arsenault OFFLINE  

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Posted May 25, 2018 - 06:05 AM

I'd say its most likely a bad switch ,but you can jump a 12 lead from the battery to the positive connection on the coil and try it....If it starts and runs fine its your key switch. 


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#3 MiCarl ONLINE  

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Posted May 25, 2018 - 06:37 AM

Your description of how it's wired doesn't sound right to me.  There should be a wire from the switch to the coil that is on a different post than the one that powers the starter solenoid.  That's how the coil is powered when you're not cranking the engine.

 

I think if you move the coil wire to the currently unused post you'll find it works.  Check with a meter to make sure the coil isn't powered with the key in the off position.

 

If you think of the 3 terminals on the switch:

 

1 = hot.

2 = coil

3 = starter solenoid.

 

With switch off none of the terminals should be interconnected.

 

With switch in the on position 1 and 2 should be connected - powering the coil so the ignition works.

 

With switch in start position all three terminals should be connected - powering the coil and energizing the starter solenoid.


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#4 firedudetl1 OFFLINE  

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Posted May 25, 2018 - 06:55 AM

try disconnecting the battery and checking continuity between the key switch and the final termination points of the wires as you turn the key to the different positions - start position should have connection between the battery and the starter, run position should have connection between the battery and the coil (assuming I'm remembering how this stuff works.... been a while....)


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#5 chieffan OFFLINE  

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Posted May 25, 2018 - 07:20 AM

You mentioned your solenoid has two small post and two large post.  Usually one of the small post is to ground the solenoid as it would be a externally grounded solenoid.  If the solenoid works with just using the one post, that part is probably OK.  MiCarl I believe has it right.  The second wire from the one terminal probably goes to power the switch for the deck clutch or the lights.


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#6 dodge trucker OFFLINE  

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Posted May 25, 2018 - 07:34 AM

ok dumb question time. does this have a battery ignition? Car type coil?  You mentioned "not being factory" wiring any more.  Has someone put a ballast resistor in the ignition lead?  In my old carb'd cars and trucks, when the ballast would go bad they would act exactly like that.  Some coils are marked "USE with EXTERNAL RESISTOR"  so need such a resistor.  Failing that I'd say the ignition switch went bad. 

Hook up an alligator clip jumper from the battery + to coil + and try to start the engine, and see what that does. 


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#7 propane1 OFFLINE  

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Posted May 25, 2018 - 09:51 AM

What type of coil, Car type or one thats mounted by the flywheel to produce spark. If car type, dodge trucker, has a good answer. 

 

Noel 



#8 MiCarl ONLINE  

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Posted May 25, 2018 - 10:53 AM

I thought about a ballast resistor or ballast wire too.  He's still not got enough wires connected to his switch for a battery ignition.  It's possible that the unused terminal had the ballast lead and it got knocked off.



#9 EricFromPa OFFLINE  

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Posted May 25, 2018 - 11:06 AM

Sounds like someone converted a points/magneto/Condenser ignition to Points/12v Coil/Condenser.  Take the wire off of the + side of the coil and run a jumper to the + side of the battery and see if it will stay running. It should.

 

There should be a 3rd wire on the old 3 prong switch to power the coil. 1 terminal wired to the battery, 1 terminal wired to the solenoid and the other terminal wired to the coil. 

 

1 power in, 1 momentary power out with the key turned to the start position and 1 will have constant power with the switch in the run position.

 

With a volt meter or test light check all 3 terminals for power. 1 from the battery will always have power. The one that has power in the run position is what you need the coil to be hooked to.



#10 captweiner OFFLINE  

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Posted May 27, 2018 - 10:09 PM

Thanks for the help....it is in the key switch.  With power hooked to middle spade....there is one of the others hot in "off", neither hot in "on", and the other one becomes hot in "start".  Not sure why one of them is hot in "off" and with none of them hot in "on" it is cutting power to the coil.  I ran a jumper wire from battery to positive on coil and tractor runs.  What is more confusing is how this tractor ran before....I think what happened is with both the coil and starter hooked to the same spade (the one that is hot in start) it was sticking in start continuously powering the starter and the coil which kept it running but also had to be hard on the starter...   The switch no longer sticks in start - so by it returning to on...it is now cutting power to the coil.  I need a new switch and I see there are 5 spades on the new one...I am assume B to Battery side of solenoid, S to the starter post of Solenoid and M to the coil?  Thanks for all the help!






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